Rolling-lobe air springs have been widely used with success as motor-vehicle springs and especially for suspending the wheel axles of trucks and buses. The flexible member of the air spring is attached at one end to a roll-off piston which is usually made of metal or plastic. In the operating state, the piston moves within the flexible member which is pushed over the roll-off piston so that the flexible member defines a rolling lobe which rolls over the outer surface of the roll-off piston.
The reinforcement layer takes up the forces which occur because of the overpressure in the flexible member of the air spring. The cord fabric layer in air-spring flexible members preferably is made of fully synthetic fibers such as nylon. The so-called cord fabric is produced from the textile cord threads. The cord fabric comprises a multiplicity of cord threads in warp direction lying parallel one next to the other. The cord threads are held loosely together at greater distances by a few thin threads in weft direction. This cord fabric layer is rubberized with a suitable rubber mixture such as a polychloroprene mixture and, after being cut at an angle, is built into the air-spring flexible member with two, four or six layers so that the threads lie crosswise. Depending upon the air spring type, the textile cord threads of the two cord fabric sheets define a symmetrical thread angle of approximately 40.degree. to 80.degree. with respect to the peripheral direction.
Cord fabrics can transmit only forces in one direction. For this reason, the rolling-lobe air spring has a symmetrical arrangement of the cord fabric layers, that is, two, four or six fabric layers which mutually cross. Most air springs for street motor vehicles are, however, produced only with two mutually crossing fabric layers in order to achieve a high flexibility of the flexible member of the rolling-lobe air spring.
Recent developments in motor vehicles and chassis, especially in the area of passenger cars, require increasingly smaller air spring types having correspondingly increasing operating pressures. The space available for building in the air spring is minimal in a passenger vehicle. The rolling-lobe air springs can therefore only have a small diameter and have small bending radii in the roll-off zone. The small rolling-lobe air springs therefore require the use of especially valuable elastomeric materials.
The two-layer configuration of the reinforcement layer for these small air spring types of the passenger vehicle area is no longer adequate because the air springs must withstand higher pressures during operation, such as 10 bar and higher. In order to withstand the higher operating pressures, it would be conceivable to arrange four or six cord fabric layers men the wall of the flexible member. Because of the small configuration of the rolling-lobe air spring, the strengthened reinforcement layers must, however, be very thin because a greatly reduced roll-off radius is present and thicker reinforcement layers can lead to a destruction of the wall defined by the flexible member of the air spring. This is caused, for example, in a four-layer reinforcement layer in that the threads of the inner-lying cord fabric layer becomes bunched and are destroyed. This leads to a greatly reduced strength of the rolling-lobe air spring.